Anode bushing for metal-vapor arc converters



Jan. 19, 1943. E A. SIEMENS ETAL 2,308,939

ANODE BUSHING FOR METAL-VAPOR ARC CONVERTERS Filed May 20, 1941 xwm1 fiE. 4P I LA/L WITNESSES: INVENTOR 5 KMJW ATTORNEY Patented Jan. 19, 1943UNITED STATES PATENT OFFICE ANODE BUSHING FOR METAL-VAPOR ARC CONVERTERSApplication May 20, 1941, Serial No. 394,309 In Germany February 2, 19403 Claims.

Our invention relates to an anode bushing for metal-vapor arcconverters-more in particular: high-voltage arc converters-comprising aninsulator having a tubular extension through which the anode stempasses. Known anode bushings of this kind have the disadvantage that atthe point where the anode stem leaves the tube of insulating material,high field concentrations are found which may lead to undesirableionization phenomena. Known anode-bushing arrangements have often inaddition the disadvantage that the insulating material is in contactwith the hot anode body, and that as a consequence hereof, the structureof the insulating material may be destroyed.

The present invention avoids said difiiculties in the case of an anodebushing for metal-vapor arc converters comprising a tube of insulatingmaterial through which the anode stem passes. The novelty covered by theinvention consists in the fact that there is mounted between the anodebody and the tube of insulating material a tube of graphite whichsurrounds the spot at which the anode stem leaves the tube of insulatingmaterial.

Application of the invention has the following beneficial results: inthe first place, the tube of graphite constitutes a thermally insulatingshield between the anode body and the tube of insulating materialthrough which the anode stem must pass, and, in the second place. fieldconcentrations at the point where the anode stem leaves the tube ofinsulating material will be avoided. In connection herewith, it is ofadvantage to reduce the outer diameter of the tube of insulatingmaterial at the lower end of this tube, and to insert this lower endinto a corresponding recess of the graphite tube.

The invention further proposes to surround all live parts of the anodestructure-except the front surface of the anode body-with a shieldingmember whose surface is continuous all around the anode-axis, and toapply to this shielding member a definite potential, it being necessaryto arrange this member in a manner such that at any point its distancefrom the live parts will be shorter than the critical distance overwhich ionization by collision could still occur. It is desirable toapply to the shielding member a definite potential having a valuecomprised between the anode and cathode potential. Such apotential-value can be obtained, for instance, with the aid of apotential divider, or the shielding member can be connected to the anodethrough an appropriately chosen resistor.

An example of an anode bushing designed in accordance with the presentinvention is illustrated on the drawing in which the figure is insectional elevation of an anode bushing accord ing to our invention.

An anode body 2 of graphite is attached to the lower end of an anodestem l whose upper portion is surrounded by a tube 3 of insulatingmaterial. In accordance with the present invention, a tube 4 of graphiteis inserted between the anode body 2 and the tube 3 of insulatingmaterial. At its lower end 5, the tube 3 of insulating material has areduced outer diameter, and this end 5 of the tube is inserted into acorresponding recess of the tube 4 of graphite. A small air-gap 8 isleft open at the periphery of 5, between 5 and the tube of graphite.

The anode body 2 and the tube 4 of graphite are surrounded by acontinuous shielding member 6, the shielded space being shut 01f at thelower end of the shielding member 6 by a grid structure 1. It isadvantageous to have the upper portion of the shielding member 6 extendbeyond the air-gap 8 left open between the tube 3 of insulating materialand the tube 4 of graphite. The distance of the shielding member fromthe live parts 2 and 4 is shorter than the critical distance over whichionization by collision could still occur.

We claim as our invention:

1. An anode assembly for a vapor-electric arc converter comprising, ananode stem, a graphite anode head on said stem, a substantially tubularbushing of insulating material surrounding a portion of said stem, saidbushing ending in spaced relation from said anode head and asubstantially tubular body of graphite surrounding that portion of theanode stem between the anode head and the bushing, that portion of thebushing forming the end adjacent the graphite body being of lessexternal diameter than this main body of the bushing, that portion ofthe graphite body adjacent the bushing having a recess of greaterinternal diameter than the diameter of the end of the bushing, saidgraphite body being telescoped over the end of the bushing and laterallyspaced therefrom.

2. An anode bushing according to claim 1, characterized by the featurethat all live parts of the anode structure-except the front surface ofthe anode body-are surrounded by a shielding member whose surface iscontinuous all around the anode-axis and to which a definite potentialis applied, the distance of this shielding member from the live partsbeing shorter than the critical distance over which ionization bycollision could still occur.

3. In a vapor arc converter, an anode construction comprising an anodehead, an anode stem supporting the head, an insulating bushingsurrounding the stem said bushing ending in spaced relation to the head,a graphite tube 10 surrounding the stem between the bushing and thehead, a reduced portion on the end of the

